U.S. Pat. Nos. 5,458,096, 5,505,164, 5,467,745, 5,669,335, and 5,657,722 all relate to a system for controlling the flow of coolant or temperature control fluid in an engine for improving the temperature state of the engine. A system incorporating the teachings disclosed in those patents is currently being developed by Windfall Products, Inc. and is referred to as the EETC.TM. system.
The above-referenced patents, in particular, discuss the disadvantages associated with conventional thermostat regulated cooling systems. A conventional thermostat operates as a one-way valve, blocking or allowing flow of coolant to a radiator. Most prior art coolant systems employ wax pellet type or bimetallic coil type thermostats. These thermostats are self-contained devices which open and close according to precalibrated temperature values. The thermostat is mounted such that the wax pellet is located within the coolant. Thus, the state of the prior art wax pellet type or bimetallic coil type thermostats is controlled solely by coolant temperature. Other factors, such as ambient air temperature or oil temperature, cannot be taken into account when setting the state of such thermostats.
Coolant systems must perform a variety of functions in addition to cooling the engine parts. In cold weather, the cooling system must deliver hot coolant to heat exchangers associated with the heating and defrosting system so that the heater and defroster can deliver warm air to the passenger compartment and windows. The coolant system must also deliver hot coolant to the intake manifold to heat incoming air destined for combustion, especially in cold ambient air temperature environments, or when a cold engine is started. Ideally, the coolant system should also reduce its volume and speed of flow when the engine parts are cold so as to allow the engine to reach an optimum hot operating temperature. Since one or both of the intake manifold and heater need hot coolant in cold ambient air temperatures and/or during engine start-up, it is not practical to completely shut off the coolant flow through the engine block.
Practical design constraints limit the ability of the coolant system to adapt to a wide range of operating environments. For example, the heat removing capacity is limited by the size of the radiator and the volume and speed of coolant flow.
The EETC system was developed in order to rectify the deficiencies of the prior art cooling systems. The EETC system includes, in one configuration of the system, a hydraulically controlled valve which regulates flow of temperature control fluid between a water jacket surrounding the engine and a radiator. The valve has a valve member which is reciprocated between an open and closed position for controlling flow to or from the radiator. The valve is disclosed in detail in U.S. Pat. No. 5,458,096 which is incorporated herein by reference in its entirety. The system also includes a hydraulic fluid injection system which supplies pressurized fluid to the valve for controlling its opening and closing. A processor is utilized for controlling the hydraulic fluid injection system (and, thus, the state of the valve) based upon various sensed signals and one or more temperature control curves. The details of the EETC system, including the hydraulic fluid injection system, are disclosed in U.S. Pat. Nos. 5,467,745, 5,507,251, 5,638,775, 5,657,722, and 5,669,335, which are all incorporated herein by reference in their entirety.
FIGS. 1A-1C schematically illustrate the operation of the EETC system with a hydraulic EETC valve. FIG. 1A illustrates the flow of temperature control fluid through the water jacket of an engine. The flow of the temperature control fluid is depicted by the arrows. The stippling is used in the figure to represent the temperature state of the temperature control fluid (i.e., more stippling represents a higher temperature). As shown, the EETC valve V is in its closed position preventing flow of temperature control fluid to the radiator R. Instead, the temperature control fluid circulates only within the water jacket. The processor, such as an engine control unit (ECU), monitors a variety of signals, such as, for example, temperature control fluid temperature, ambient air temperature and/or engine oil temperature (generally designated by arrows S). Based on these signals, the ECU determines the temperature state of the engine. When the temperature state of the engine exceeds a threshold valve, the ECU sends a signal to a hydraulic fluid actuation system H to open the EETC valve V. The hydraulic fluid actuation system includes a pump which supplies hydraulic fluid to a solenoid communicating with the valve. FIG. 1B depicts the EETC system after the valve V has opened with the temperature control fluid flowing to and from the radiator.
FIG. 2 illustrates one embodiment of a temperature control curve for controlling the EETC valve V. The temperature control curve (identified as the "normal" curve) is shown compared with the plot of a conventional prior art thermostat. As shown, the temperature control fluid (TCF) temperature at which the valve is opened and closed varies as a function of the ambient temperature. For ambient temperatures less than 85.degree. F., the temperature control fluid temperature in the engine will run hotter than a system that uses a conventional thermostat.
As its temperature increases, the temperature control fluid will expand. The fluid expansion generates increased pressures within the engine cooling system and, in particular, within the radiator. The increased pressure within the system increases the boiling point of the temperature control fluid. This is beneficial since it allows the engine (and temperature control fluid) to operate at a higher temperature. However, if the pressure increases too much, it could cause rupture of the thin walled radiator cores found in most conventional radiators.
In order to prevent over pressurization of a cooling system, conventional engines incorporate a radiator cap RC which allows fluid to blow out of the radiator R into an overflow bottle OB when the pressure within the radiator R exceeds a pre-set value. The radiator cap RC also allows fluid to be drawn back into the radiator R when the engine cools.
Conventional radiator caps RC are designed to vent pressure from the radiator when the radiator pressure exceeds 15 psi. Testing has shown that the temperature of the temperature control fluid in the EETC system during cold ambient temperatures (e.g., less than 5.degree. C.), produces pressures within the radiator that approach and slightly exceed 15 psi. If this pressure is not relieved, damage to the radiator could result.
A need, therefore, exists for a system that dissipates pressure within the radiator during cold weather conditions in order to reduce pressurize within the radiator.